This invention relates to reaction injection molded polyurethanes, polyureas and polyurea/urethanes which are prepared using polyisocyanates and polyols. This invention also relates to compatible mixtures of high and low molecular weight polyols.
Reaction injection molded polyurea/urethanes are well-known in the art as described by F. Melvin Sweeney in Reaction Injection Molding Machinery and Processes, Marcel Dekker, Inc., 1987. The use of reaction injection molding (RIM) polyurethanes in the production of structural parts for automotive applications such as fenders, doors and body panels as well as in other applications such as computer housings, sports equipment and the like is well known.
RIM polyurea/polyurethane processes typically employ the reaction of polyisocyanate with a high equivalent weight polyhydroxyl-containing compound, optionally in the presence of a chain extender which is a low equivalent weight polyhydroxyl- or polyamine-containing compound as disclosed in U.S. Pat. Nos. 4,297,444 and 4,686,242.
U.S. Pat. No. 4,218,543 discloses a process for using specific aromatic polyamines as chain extenders in a one-shot process. These aromatic diamines are characterized as having alkyl groups in both positions ortho to one amino group and in at least one of the positions ortho to the second amino group. U.S. Pat. No. 4,374,210 discloses a similar process for the use of aromatic diamines wherein at least one of the positions ortho to each of the amino groups is substituted by a lower alkyl. One disadvantage of these processes is the limited type and number of aromatic polyamine compounds which correspond to the above descriptions.
The use of urea and certain hydrocarbyl-substituted ureas as compatibilizing agents for ethylene glycol RIM systems is disclosed in U.S. Pat. Nos. 4,485,031 and 4,485,032. However, in RIM applications, the use of urea has been associated with surface defects in the final RIM product. It would be desirable to form a compatible mixture of high and low molecular weight polyols, without resulting in surface defects in the final RIM product. It would also be desirable to expand the number of choices of aromatic polyamine compounds which may practicably be used in RIM processes.